A double glazing unit has been commonly employed as window glass for a railway vehicle in order to improve sound insulation, heat insulation and safety (see Patent Document 1 etc.). Such double glazing unit is configured by disposing an exterior-side glass plate and an interior-side glass plate through a spacer, and sealing a peripheral edge by a seal.
In the double glazing unit disclosed in Patent Document 1, a non-tempered glass plate (float glass), which has a thickness of 5 mm, has been employed as each of the exterior-side glass plate and the interior-side glass plate. By this arrangement, the double glazing unit has a strength set to a level appropriate to window glass for a railway vehicle.
Further, the exterior-side glass plate of the double glazing unit disclosed by Patent Document 1 has a self-dimming film disposed thereon. The self-dimming film is deposited on one of the two sides of the exterior-side glass plates facing the interior-side glass plate by sputtering. The self-dimming film has a function of setting the transmittance of visible light at from 70 to 90% when the light intensity from outside is low and of setting the transmittance of visible light at from 50 to 70% when the light intensity from outside is high.